Immunohistochemical evidence of the presence of synaptic contacts in a newly generated PG cell. a, Confocal images combined to produce a three-dimensional reconstruction of a synapse on a newborn neuron. The GFP+ PG cell shown (green) is from a P34 animal, 24 d after virus injection (red, synapsin). The center image is a maximum intensity projection with orthogonal “x-z” and “y-z” views on the side to show close apposition of the PG cell process with synapsin puncta from the point indicated by the crossed lines. The image consists of 22 optical sections, each section being 0.9 μm thick. Scale bar, 8 μm. An enlargement of the synaptic contact at the center of the cross lines (arrow) is shown in the bottom right corner. b, GFP+ PG cell in a 121-d-old animal (virus injected at P87). The red dye marks the presynaptic protein SV2. The insets show strong colocalization (yellow) of the marker with GFP. Note that in b1 the synapse may actually be a dendrodendritic one. Arrowheads point to SV2 labeling within and just outside the dendrite terminal with a faint gap that is barely perceptible, dividing the two regions. Scale bars, 20 and 3 μm. c, Expression of the glutamate receptor GluR1 subunit (red) in a GFP+ PG cell (green); coexpression is indicated in yellow. Confocal images combined to produce a maximum intensity projection of a newborn neuron (inset). The PG cell shown is from a P52 animal (37 d survival). The center image is a two-channel single-optical section overlay with orthogonal x-z and y-z views along the indicated lines. The image consists of 24 optical sections, each section being 1 μm thick. Scale bar, 20 μm.